1. Technical Field
The invention generally relates to an apparatus for heating the air/fuel mixture entering the cylinders of an internal combustion engine. More particularly, the invention relates to an electric heater element having a resistance that may be varied to suit specific applications.
2. Discussion
The air/fuel mixture entering the cylinders of an internal combustion engine is commonly heated to increase fuel economy and responsiveness to starting as well as to decrease pollutant discharge. One type of intake heating device generally includes a heating element or coil electrically connected to a power source and disposed in the intake air passageway of an engine. In the afore-referenced device, current is passed through the heating element or coil to increase the temperature of the surrounding air as it enters the air intake manifold.
While the aforementioned heaters generally address cold starting and fuel economy issues, other concerns remain. One concern is design flexibility. For example, if a heating element is electrically connected to a power source with a fixed voltage supply, such as a vehicle battery, the element emits a fixed amount of heat energy. However, the amount of heat required can vary depending upon the specific heater application. Factors such as ambient air temperature, engine displacement, intake air passageway cross-sectional area and intake gas volume flow rate influence the amount of heat energy required to raise the air/fuel mixture temperature. Accordingly, a manufacturer may wish to vary the amount of heat energy or wattage dissipated from a heater without varying the supply voltage. This is especially true in heater applications for motor vehicles where one portable battery supplies power to the vehicle and varying the voltage supplied to the heater is cumbersome and expensive.
In general, a manufacturer of prior art heaters was afforded minimal control over the resistance of a heating element. Known methods of varying the resistance include modifying the thickness and/or the length of the element. As such, heaters of different capacities often required heating elements of vastly different geometry. As would be expected, the components designed to cooperate with the heating elements were also required to change. For example, an increase in length often required a corresponding change in insulators. A change in the insulators often forced a change in the holders or other retention device. Ultimately, the use of a different heating element could ripple throughout the entire design, possibly requiring a proportionately sized housing and intake opening.
Accordingly, prior heaters equipped with fixed resistance heating elements may be improved upon to provide the additional design flexibility of variable power output. Specifically, one practicing the disclosed invention may vary resistance without changing the external dimensions of the element thereby allowing different heating capacities in the same heater housing. Original equipment manufacturers attempting to reduce component inventory by using one heater in a variety of different applications will find use for such an improved heater.
Another concern exists as to the temperature homogeneity of the heated air as it enters the combustion chamber. It is desirous to produce a uniformly heated volume of air in order to enhance cold starting conditions and efficient combustion. Existing heater designs simply allow the unheated air to pass by round wires or flat element sections in a generally laminar manner. Heat transfer from the heating element to the air may be increased through the introduction of turbulent flow.
In view of the above concerns as well as the manufacturer's ever present desire to reduce manufacturing costs and complexity, a need exists for a heater element with variable resistance that may be inexpensively manufactured, and utilized in a variety of applications. Additionally, a need exists for a heater that produces a more uniformly heated supply of air to the engine.